I added a new tab in my TaskEditor, with 5 fields (two combobox, two checkboxfield, and a textfield) for custom task data. I have two questions:

1. How do I get them to populate from data saved in my task?
2. How do I get them to save data to my task?

When I click save, and have edited those fields, it just closes the window, without any save. I saw on one of the forum posts that I should use loadtask and afterupdatetask, but the documentation for these is a bit sparse so I am not sure how to use them.

To populate fields 'loadtask' event can be used. It receives task being loaded as an argument.
So idea is to get values from task data and put them to fields that you have created. Something like this:

Thank you! Your example was really helpful. It works great for my textfield but is having some trouble with the checkbox and the combobox. It will load the checkbox but regardless or checked or not it gets saved as null. The combo box just saves 0 and doesn't load the selected value. Any help would be greatly appreciated!

The Franchise combobox and the Staff combobox all have their own store that populates the list. Here is the model used for it. I want to store the actual ID, not the name (but have the name displayed in the box).

Here is 'name' must specify your custom attribute of the task. So it defines task field where selected value will be stored.
And 'displayField' and 'valueField' must point to the attributes of the selection list record (must point to fields of StaffMember model in this case). But instead valueField points to 'NotifyUSRAdminUsers_ID'. There probably should be 'USRAdminUsers_Id' column. And the same problem with other combobox ..property points to wrong column.

I'm really suspicious about 'inputValue' config. Why is it set to 'NotifyClient'?
This setting means that when checkbox is selected then field value must be set to 'NotifyClient' string.
I mean it can work of course if you defined NotifyClient column type as string ..no problem.
Still it's kind of odd for me. For such type of fields values like 1, "on", true are used normally.
What's the type of NotifyClient column? ..And the same thing is for all checkboxes.
Actually after I set combobox columns as I said everything started to work for me.

The column NotifyClient is boolean. I tried setting inputValue: 1, but it still saved as null. I want it to get the value from the NotifyClient column (0 or 1) and set it according to whether or not it is checked. I thought inputValue was the right one but maybe not.

For general information please checkout the docs. You can find how to load/save data at the top of the page. Also our Advanced demo has a custom field in the task editor, so you can look at the demo sources to check how it works.